The present invention relates to an electric power conversion apparatus, such as a converter and an inverter.
A power conversion apparatus having a structure of a built-in three phase ac sine wave input converter is disclosed in JP-A No. 6-335254, in which an uninterruptible power supply is described. This power conversion apparatus is comprised of a circuit which includes: switching devices in bridge connection which are coupled to a three phase ac power supply via a reactor; a capacitor coupled to the output of the converter for producing a dc voltage; a pulse wave generator for generating a pulse wave in synchronism with the power supply voltage across these switching devices in bridge connection using the dc voltage; and means for conducting a sine wave current through the reactor in synchronism with the phase voltage of the power supply by controlling the pulse wave, thereby reducing harmonic components contained in the input current.
In the above described power conversion apparatus having a three phase ac input and a sine wave input converter which controls an input current to become a sine wave in synchronism with an input voltage, and an inverter which outputs an ac voltage which is in synchronism with the input power voltage, there is a problem in that prior to coupling the electric power conversion apparatus to the three phase ac power supply, it was necessary to determine the direction of phase rotation in advance, and then to couple the apparatus in the phase sequence as designated. This procedure is required in order to synchronize the power synchronizing circuit within the electric power conversion apparatus with the frequency and phase of the input power supply. Hence, when the apparatus is coupled in an antiphase configuration, it is not able to operate normally due to the out-of-phase condition. However, it is difficult to determine whether the phase sequence is correct or not until the apparatus is actually started, and this has been one of the factors which prevented easy handling of the electric power conversion apparatus.